The present invention relates to an apparatus for purifying blood, which is useful for eliminating unnecessary or impure substances from the blood of a patient and purifying the blood.
In recent years, as a method for purifying the blood, a method has been broadly used, in which plasma is separated from blood, unnecessary substances are eliminated from the plasma to purify it, and then, the purified plasma is returned into a patient body.
The above method has advantages that there is no possibility of infection in comparison with a plasma-exchange treatment and that a loss and a damage of blood cells are less in comparison with a direct hemoperfusion treatment, in which blood is directly contacted with a purifier or the like to eliminate the unnecessary substances.
The method consists of three processes, i.e. a process for separating blood into plasma and blood rich in blood cells (a plasma-separating process), a process for purifying the plasma by passing through a purifying device to eliminate the unnecessary substances (a purifying process) and a process for mixing the purified plasma with the blood rich in blood cells (a mixing process).
A continuous centrifugation or a porous membrane can be used in the plasma-separating process to separate the blood, and recently, a plasma-separator employing a porous hollow fiber which is relatively easy to handle has been broadly used. However, even in those cases, scrupulous attention must be paid at the beginning of a blood circulation outside the body (a priming period), and an operation is necessary, that a plasma filtration rate is gradually increased to a steady state with controlling a balance between the plasma filtration rate and the blood flow rate. If such an operation is faultily handled, various problems such as hemolysis and blocking of the membrane will be caused. Such problems will eventually cause the decrease of plasma filtration rate. Further, it is necessary to maintain a trans membrane pressure within a definite range, and when it is neglected, the same problems as described above will also occur. As mentioned hereinbefore, a conventional plasma-separating process has a drawback that its operation is complicated and skilled technics are required for the operation.
In the purifying process, a removing device is used to eliminate the unnecessary substances which consists of a container charged with a purifying agent such as an ion exchange resin or an immunological adsorbent or an adsorbent prepared by fixing a material having an affinity for the unnecessary substances to a water-insoluble carrier. However, a conventional apparatus for purification of blood such as the apparatus disclosed in Japanese Examined Patent Publication (Tokkyo Kokoku) No. 22107/1980 has several problems. Hereinafter, the problems are explained with reference to FIG. 1.
FIG. 1 is a block diagram showing a conventional apparatus for a purification of blood, wherein a blood-circulating pump 1, a plasma separator 2, a plasma pump 3, a plasma purifying device 4 and a mixing vessel 5 are connected so that the blood flows into the separator 2 like an arrow A and flows out from the vessel 5 like an arrow B.
Plasma separated at the separator 2 is transferred to the purifying device 4 by means of the pump 3, whereby the plasma has only one chance to contact with a plasma purifier in the device 4 after separated from the blood. It is not until the time when the plasma is mixed with blood rich in blood cells at the mixing vessel 5, and the blood is once returned into a body, taken out from the body again and subjected to a separation at the separator 2, and then, the separated plasma is transferred to the device 4 again, that the plasma which is not sufficiently purified can come in the next contact with the purifier.
Consequently, as long as employing the circulating path as shown in FIG. 1, for the purpose of improving the purification efficiency, there is no other way except that a purifier having an extremely good purification ability is used, that a large amount of a purifier is charged in the device or that a contact time is increased by lowering the taking speed of plasma. However, when a purifier is charged in the device in a large amount, an amount of blood and plasma outside the body is increased during the circulation, and a patient is exposed to a dangerous condition. When the plasma flow rate is lowered, a treating time becomes longer and it is disadvantageous. Therefore, a purifier usable in the purifying apparatus described above is limited to a purifier which has a high purification rate.
Moreover, the purifying apparatus shown in Fig. 1 has a serious problem that there is a danger that the purifier flows into the blood stream. As the purifier, a purifier in the form of particle is generally used, and there is a possibility that purifier particles or the broken pieces thereof leak from the purifying device 4 by the plasma current and flow into the blood on the plasma current. For the purpose of avoiding such a danger, it is required to provide a filter at an inlet and an outlet of the purifying device.